U.S. patent application number 17/684806 was filed with the patent office on 2022-09-22 for image forming apparatus.
The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Kazuhiro Doda.
Application Number | 20220299914 17/684806 |
Document ID | / |
Family ID | 1000006214708 |
Filed Date | 2022-09-22 |
United States Patent
Application |
20220299914 |
Kind Code |
A1 |
Doda; Kazuhiro |
September 22, 2022 |
IMAGE FORMING APPARATUS
Abstract
An image forming apparatus includes a fixing unit including a
tubular film, a pressure roller, and a heater including a heating
element. The apparatus further includes a control unit configured
to calculate an accumulated electrical energy supplied to a portion
of the heating element. The portion of the heating element is
located in an area corresponding to a second area of the nip
portion. The second area is an area of the nip portion through
which the recording material conveyed to the nip portion is not
passed. The control unit is configured to determine an operation of
heat leveling, which is performed for leveling a heat distribution
in the nip portion after the recording material had passed the nip
portion, based on the calculated accumulated electrical energy.
Inventors: |
Doda; Kazuhiro; (Kanagawa,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
1000006214708 |
Appl. No.: |
17/684806 |
Filed: |
March 2, 2022 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03G 15/2039
20130101 |
International
Class: |
G03G 15/20 20060101
G03G015/20 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2021 |
JP |
2021-040563 |
Claims
1. An image forming apparatus comprising: a fixing unit including a
tubular film, a pressure roller abutting against an outer
circumference surface of the film to form a nip portion, and a
heater including a heating element, wherein the fixing unit is
configured to fix a toner image to a recording material by heating
the toner image on the recording material with the heater at the
nip portion; and a control unit configured to calculate an
accumulated electrical energy supplied to a portion of the heating
element, wherein the portion of the heating element is located in
an area corresponding to a second area of the nip portion, wherein
a first area of the nip portion is an area through which the
recording material conveyed to the nip portion is passed and the
second area of the nip portion is an area through which the
recording material conveyed to the nip portion is not passed, and
wherein the control unit is configured to determine an operation of
heat leveling, which is performed for leveling a heat distribution
in the nip portion after the recording material had passed the nip
portion, based on the calculated accumulated electrical energy.
2. The image forming apparatus according to claim 1, wherein the
heater is configured to be supplied power from an AC power
supply.
3. The image forming apparatus according to claim 2, further
comprising a switch configured to connect and disconnect a power
supply path from the AC power supply to the heater, wherein the
control unit is configured to output a control signal for
controlling the switch every half cycle of a power supply frequency
of the AC power supply.
4. The image forming apparatus according to claim 3, further
comprising: a voltage detection unit configured to detect voltage
applied to the heater by the AC power supply; and a current
detection unit configured to detect a current flowing from the AC
power supply to the heater, wherein the control unit is configured
to calculate the accumulated electrical energy supplied to the
portion of the heating element corresponding to the second area,
based on a voltage value detected by the voltage detection unit, a
current value detected by the current detection unit, a length in a
direction orthogonal to a conveyance direction of the recording
material passed through the nip portion, and a length of the heater
in a longitudinal direction.
5. The image forming apparatus according to claim 4, wherein an
electrical energy supplied to the heating element is calculated
based on the voltage value and the current value.
6. The image forming apparatus according to claim 3, wherein the
control unit is configured to calculate the accumulated electrical
energy supplied to the portion of the heating element corresponding
to the second area, based on an electrical energy supplied to the
heating element during a half cycle of the power supply frequency,
a number of control signals output to connect the power supply path
to the heater, a length in a direction orthogonal to a conveyance
direction of the recording material passed through the nip portion,
and a length of the heater in a longitudinal direction.
7. The image forming apparatus according to claim 6, wherein the
electrical energy supplied to the heating element during the half
cycle of the power supply frequency is calculated based on a
voltage value of the AC power supply and a resistance value of the
heating element.
8. The image forming apparatus according to claim 2, wherein the
heater includes a plurality of heating elements having different
lengths in a longitudinal direction; wherein the image forming
apparatus further comprises a plurality of switches configured to
connect and disconnect power supply paths from the AC power supply
to the plurality of heating elements, and wherein the control unit
is configured to perform power supply to the plurality of heating
elements every half cycle of a power supply frequency of the AC
power supply by outputting a control signal for controlling the
plurality of switches in accordance with a length in a direction
orthogonal to a conveyance direction of the recording material
passed through the nip portion.
9. The image forming. apparatus according to claim 8, wherein the
control unit is configured to control the plurality of switches
such that power supply to two or more heating elements will not be
performed during each half cycle of the power supply frequency.
10. The image forming apparatus according to claim 9, further
comprising a temperature detection unit configured to detect a
temperature of the heater at a time when printing of the recording
material is started, wherein the control unit is configured to
determine proportions of power supply to a first heating element
and to a second heating element among the plurality of heating
elements, the second heating element having a length in the
longitudinal direction shorter than the first heating element, a
length in a direction orthogonal to a conveyance direction of the
recording material passed through the nip portion being closer to
the length of the second heating element than to the length of the
first heating element.
11. The image forming apparatus according to claim 10, wherein the
proportion of power supply to the first heating element increases
as a temperature of the heater detected by the temperature
detection unit becomes lower, and the proportion of power supply to
the second heating element increases as a temperature of the heater
detected by the temperature detection unit becomes higher.
12. The image forming apparatus according to claim 11, wherein the
control unit is configured to calculate an accumulated electrical
energy supplied to a portion of the first heating element and a
portion of the second heating element each located in the area
corresponding to the second area of the nip portion, based on an
electrical energy supplied to the first heating element during a
half cycle of the power supply frequency, a number of control
signals output to connect a power supply path to the first heating
element, an electrical energy supplied to the second heating
element during a half cycle of the power supply frequency, a number
of control signals output to connect a power supply path to the
second heating element, a length in a direction orthogonal to a
conveyance direction of the recording material passed through the
nip portion, a length in the longitudinal direction of the first
heating element, and a length in the longitudinal direction of the
second heating element.
13. The image forming apparatus according to claim 12, wherein the
electrical energy supplied to the first heating element during the
half cycle of the power supply frequency is calculated based on a
voltage value of the AC power supply and a resistance value of the
first heating element, and wherein the electrical energy supplied
to the second heating element during the half cycle of the power
supply frequency is calculated based on the voltage value of the AC
power supply and a resistance value of the second heating
element.
14. The image forming apparatus according to claim 5, further
comprising a temperature calculation unit configured to calculate a
temperature of the film in the second area, and wherein the
temperature calculation unit is configured to use a first
calculation formula, by which the temperature of the film in the
second area is calculated based on the accumulated electrical
energy calculated by the control unit.
15. The image forming apparatus according to claim 14, wherein the
temperature calculation unit is configured to use a second
calculation formula, by which a saturation temperature of the film
in the second area is calculated based on a change rate per time of
the accumulated electrical energy calculated by the control unit,
and wherein in a case where a temperature of the film in the second
area calculated by the first calculation formula is higher than the
saturation temperature calculated by the second calculation
formula, the temperature calculation unit is configured to set the
saturation temperature as the temperature of the film in the second
area.
16. The image forming apparatus according to claim 13, further
comprising a temperature calculation unit configured to calculate a
temperature of the film in the second area, and wherein the
temperature calculation unit is configured to use a third
calculation formula, by which a saturation temperature of the film
in the second area is calculated based on the proportions of power
supply to the first heating element and to the second heating
element, and wherein the temperature calculation unit is configured
to set the saturation temperature calculated by the third
calculation formula as a temperature of the film in the second
area.
17. The image forming apparatus according to claim 15, wherein the
control unit is configured to retain information associating a
temperature of the film in the second area with a cooling time of
the film for lowering the temperature of the film in the second
area to a predetermined temperature, and wherein the control unit
is configured to determine the cooling time of the film based on
the information and the temperature of the film in the second area
calculated by the temperature calculation unit.
18. The image forming apparatus according to claim 1, wherein the
control unit is configured to stop the pressure roller for a period
of time in which the operation of heat leveling is executed, or to
drive the pressure roller for the period of time.
19. The image forming apparatus according to claim 1, wherein the
heater is arranged in an interior space of the film, the film being
nipped by the heater and the pressure roller, and the toner image
on the recording material is heated by the film at the nip portion.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to image forming apparatuses
equipped with a fixing unit.
Description of the Related Art
[0002] Electrophotographic image forming apparatuses such as a
laser printer, a copying machine, or a facsimile are equipped with
a fixing unit for fixing a toner image transferred to a recording
material. A film-heating-type fixing unit is composed of a fixing
film and a pressure roller that comes into contact with the fixing
film, and a heater substrate is provided in the fixing film. The
film-heating-type fixing unit has a low heat capacity, so that when
power is supplied to the heater substrate, parts such as the fixing
film can be heated to a predetermined temperature condition in a
short time. Therefore, the film-heating-type fixing unit is a
fixing unit that has an advantageously short first printout time
(FPOT).
[0003] Meanwhile, in a case where recording materials having a
small sheet width, which is a length in a direction orthogonal to a
conveyance direction, are passed through the fixing unit
continuously, a non-sheet-passing portion, which is an area of the
fixing film and the pressure roller where the recording material
does not pass, reaches a higher temperature compared to a
sheet-passing portion, which is an area where the recording
material passes. In this state, if a recording material having a
large sheet width passes the fixing unit, the recording material
will be in an excessively heated state at the area corresponding to
the non-sheet-passing portion of the fixing film, and image defects
such as hot offsets may occur
[0004] For example, Japanese Patent Application Laid-Open
Publication No. H11-73055 proposes a method of avoiding the
occurrence of hot offsets. In the image forming apparatus
illustrated in Japanese Patent Application Laid-Open Publication
No. H11-73055, a number of recording materials having a small sheet
width that had passed through the fixing unit is counted, wherein
if a count value exceeds a certain number, a period of rotation of
a pressure roller is increased to cool the fixing unit after the
recording material having a small sheet width had passed through.
Thereby, a temperature of the non-sheet-passing portion of a fixing
member of the fixing unit is lowered, and the occurrence of hot
offsets can be avoided even if a large-size recording material is
passed through the fixing unit after the small-size recording
material had passed through.
[0005] However, according to the method proposed in Japanese Patent
Application Laid-Open Publication No. H11-73055 mentioned above,
there may be a case in which the method cannot respond flexibly to
grammage, i.e., weight per unit area, of the recording material or
change of sheet width of the recording material. For example, in a
case where the grammage of the recording material is great, that
is, the recording material is heavy, electric power supplied to a
heater serving as a heat source becomes high, and electric power
supplied to the non-heat-passing portion of the heater also becomes
high, so that the speed of rising of the temperature of the
non-sheet-passing portion becomes fast. Further, since the electric
energy supplied to the non-sheet-passing portion of the heater
becomes high, the temperature of the non-passing-portion of the
fixing member, i.e., fixing film, rises. Meanwhile, if the grammage
of the recording material is small, that is, the recording material
is light, the electric power supplied to the heater serving as the
heat source is low, and the electric power supplied to the
non-sheet-passing portion becomes low, so that the speed of rising
of temperature of the non-sheet-passing portion becomes slow.
Further, if the sheet width of the recording material is small, the
electric power supplied to the non-sheet-passing portion becomes
high, and the speed of rising of temperature of the
non-sheet-passing portion becomes fast. Meanwhile, if the sheet
width of the recording material is great, the electric power
supplied to the non-sheet-passing portion becomes small, and the
speed of rising of temperature of the non-sheet-passing portion
becomes slow.
[0006] According to the image forming apparatus of Japanese Patent
Application Laid-Open Publication No. H11-73055 mentioned above, as
the number of sheets of recording material having passed through
the fixing unit increases, the period of rotation of the pressure
roller abutting against the fixing member is increased to cool the
fixing member, i.e., fixing film, of the fixing unit. However,
according to this method, it is difficult to deal with the
differences in temperature rising speed of the non-sheet-passing
portion caused by the differences in grammage or width of the
recording material. Therefore, if the temperature rising speed of
the non-sheet-passing portion is too fast, hot offsets may occur,
whereas if the temperature rising speed is too slow, the period of
rotation of the pressure roller for cooling the fixing member,
i.e.. fixing film, will be performed longer than necessary.
SUMMARY OF THE INVENTION
[0007] According to one aspect of the invention, an image forming
apparatus includes a fixing unit including a tubular film, a
pressure roller abutting against an outer circumference surface of
the film to form a nip portion, and a heater including a heating
element, wherein the fixing unit is configured to fix a toner image
to a recording material by heating the toner image on the recording
material with the heater at the nip portion, and a control unit
configured to calculate an accumulated. electrical energy supplied
to a portion of the heating element, wherein the portion of the
heating element is located in an area corresponding to a second
area of the nip portion, wherein a first area of the nip portion is
an area through which the recording material conveyed to the nip
portion is passed and the second area of the nip portion is an area
through which the recording material conveyed to the nip portion is
not passed, and wherein the control unit is configured to determine
an operation of heat leveling, which is performed for leveling a
heat distribution in the nip portion after the recording material
had passed the nip portion, based on the calculated accumulated
electrical energy.
[0008] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a cross-sectional view illustrating a
configuration of an image forming apparatus according to first to
fourth embodiments.
[0010] FIG. 2 is a block diagram illustrating a configuration of a
control unit of the image forming apparatus according to the first
to fourth embodiments.
[0011] FIGS. 3A and 3B are each a cross-sectional view illustrating
a configuration of a fixing unit according to the first to fourth
embodiments.
[0012] FIG. 4A is a view illustrating a configuration of a heater
according to the first embodiment.
[0013] FIG. 4B is an explanatory view of a power supply path of the
heater according to the first embodiment.
[0014] FIG. 5 is an explanatory view of a positional relationship
between a heater and a sheet according to the first embodiment.
[0015] FIG. 6A is a view illustrating a relationship between a
risen temperature value of a non-sheet-passing portion and a
temperature rising time according to the first embodiment.
[0016] FIG. 6B is a view illustrating a relationship between an
accumulated electrical energy of the non-sheet-passing portion and
the temperature rising time according to the first embodiment.
[0017] FIG. 7A is a graph illustrating a relational expression 1
according to the first embodiment.
[0018] FIG. 7B is a graph illustrating a relational expression 2
according to the first embodiment.
[0019] FIG. 8 is a graph illustrating a relational expression 3
according to the first embodiment.
[0020] FIG. 9 is a flowchart illustrating a control sequence for
cooling the fixing unit according to the first embodiment.
[0021] FIG. 10A is an explanatory view illustrating a power supply
path according to a second embodiment.
[0022] FIG. 10B is an explanatory view illustrating a relationship
between a power supply quantity and a control signal according to
the second embodiment.
[0023] FIG. 11A is a view illustrating a heater configuration
according to a third embodiment
[0024] FIG. 11B is a view illustrating a power supply path of the
heater according to the third embodiment.
[0025] FIGS. 12A and 12B are each an explanatory view illustrating
a positional relationship between a heating element and a sheet
according to the third embodiment.
[0026] FIG. 13 is an explanatory view illustrating a relationship
between a power supply quantity and a control signal according to
the third embodiment.
[0027] FIG. 14A is a view illustrating a relationship between an
accumulated electrical energy and a temperature rising time of a
non-sheet-passing portion according to the third embodiment.
[0028] FIG. 14B is a view illustrating a relational expression 3
according to the third embodiment.
[0029] FIGS. 15A and 15B are explanatory views illustrating a
relational expression 4 according to a fourth embodiment.
[0030] FIG. 16 is a flowchart illustrating a control sequence for
cooling a fixing unit according to the fourth embodiment.
DESCRIPTION OF THE EMBODIMENTS
[0031] Embodiments of the present disclosure will now be described
in detail with reference to the drawings. In the following
description, passing a sheet, or sheet-passing, refers to passing a
recording material through a fixing nip portion of a fixing unit.
Further, within an area in which a heating element generates heat,
an area where the recording material does not pass is called a
non-sheet-passing area, or non-sheet-passing portion, and the area
where the recording material passes is called a sheet-passing area,
or sheet-passing portion. Further, a phenomenon in which the
temperature of the non-sheet-passing area becomes higher than the
sheet-passing area is called a temperature rise in
non-sheet-passing portion.
First Embodiment
General Configuration of Image Forming Apparatus
[0032] FIG 1 is a cross-sectional view illustrating a configuration
of a color image forming apparatus adopting an in-line system,
which serves as one example of an image forming apparatus equipped
with a fixing unit according to the first embodiment. A
configuration of an electrophotographic color image forming
apparatus will be described with reference to FIG. 1. A first
station is a station for forming a yellow (Y) toner image, and a
second station is a station for forming a magenta (M) toner image.
A third station is a station for forming a cyan (C) toner image,
and a fourth station is a station for forming a black (K) toner
image.
[0033] In the first station, a photosensitive drum 1a serving as an
image bearing member is an organic photoconductor (OPC)
photosensitive drum. The photosensitive drum 1a is formed by
laminating multiple layers of functional organic materials
including, for example, a carrier generation layer formed on a
metal cylinder and generating charge by exposure, and a charge
transport layer for transporting generated charge, wherein an
outermost layer has a low electrical conductivity and is
approximately insulated. A charging roller 2a serving as a charging
unit abuts against the photosensitive drum 1a, and it is rotated
along with a rotation of the photosensitive drum 1a to uniformly
charge a surface of the photosensitive drum 1a. A voltage having
superposed a DC voltage or an AC voltage is applied to the charging
roller 2a, and a discharge occurs in a minute air gap formed
upstream and downstream, in a direction of rotation of the
photosensitive drum 1a, of a nip portion between the charging
roller 2a and the photosensitive drum 1a, thereby the
photosensitive drum 1a is charged. A cleaning unit 3a, is a unit
for cleaning toner remaining on the photosensitive drum 1a after
performing transfer described below. A developing unit 8a serving
as a developing unit accommodates nonmagnetic one-component toner
5a and includes a developing roller 4a and a developer application
blade 7a The photosensitive drum 1a, the charging roller 2a, the
cleaning unit 3a, and the developing unit 8a are accommodated in an
integrated process cartridge 9a that is detachably attached to the
image forming apparatus.
[0034] An exposing unit 11a, serving as an exposure unit is
composed of a scanner unit that reflects laser light by a rotary
polygon minor and scans the surface of the photosensitive drum 1a
or of a light emitting diode (LED) array and irradiates a scanning
beam 12a modulated based on an image signal to the surface of the
photosensitive drum 1a. Further, the charging roller 2a is
connected to a charging high-voltage power supply 20a serving as a
voltage supply unit for the charging roller 2a. The developing
roller 4a is connected to a developing high-voltage power supply
21a serving as a voltage supply unit to the developing roller 4a. A
primary transfer roller 10a is connected to a primary transfer
high-voltage power supply 22a serving as a voltage supply unit to
the primary transfer roller 10a. The above description illustrates
the configuration of the first station, and the second, third, and
fourth stations adopt a similar configuration. The components of
the other stations that have the same functions as the first
station are denoted with the same reference numbers, and suffix b,
c, and d are added to the reference numbers for the respective
stations. In the present description, unless a specific station is
described, the suffixes a, b, c, and d are omitted.
[0035] An intermediate transfer belt 13 is supported by three
rollers that serve as stretching members, which are a secondary
transfer opposing roller 15, a tension roller 14, and an auxiliary
roller 19. A force in a direction tensioning the intermediate
transfer belt 13 is applied via a spring (not shown) only to the
tension roller 14, so that an appropriate tension force is
maintained in the intermediate transfer belt 13. The secondary
transfer opposing roller 15 rotates by receiving rotational drive
from a main motor (not shown), by which the intermediate transfer
belt 13 wound around an outer circumference thereof is rotated. The
intermediate transfer belt 13 moves at approximately a same speed
in an arrow direction (for example, a clockwise direction in FIG.
1) with respect to the photosensitive drums 1a to 1d (which rotate
in a counterclockwise direction in FIG. 1, for example). Further, a
primary transfer roller 10 is arranged at a position opposing the
photosensitive drum 1 interposing the intermediate transfer belt
13, and it is driven to rotate following the movement of the
intermediate transfer belt 13. A position at which the
photosensitive drum 1 and the primary transfer roller 10 abut
against each other interposing the intermediate transfer belt 13 is
referred to as a primary transfer position. The auxiliary roller
19, the tension roller 14, and the secondary transfer opposing
roller 15 are electrically grounded. Further, also according to the
second to fourth stations, the primary transfer rollers 10b to 10d
adopt a similar configuration as the primary transfer roller 10a,
so that the descriptions thereof are omitted.
[0036] Next, an image forming operation according to the image
forming apparatus illustrated in FIG. 1 will be described. When a
print command is received during standby, the image forming
apparatus starts an image forming operation. The photosensitive
drum 1 and the intermediate transfer belt 13 start to rotate in the
arrow direction in the drawing at a predetermined processing speed
by a main motor (FIG. 2). The photosensitive drum 1a, is charged
uniformly by the charging roller 2a to which voltage has been
applied from the charging high-voltage power supply 20a, and
thereafter, an electrostatic latent image is formed based on an
image information by a scanning beam 12a irradiated from the
exposing unit 11a. Toner 5a inside the developing unit 8a is
charged to negative polarity by the developer application blade 7a
and applied to the developing roller 4a. A predetermined developing
voltage is applied from the developing high-voltage power supply
21a to the developing roller 4a. In a state where the
photosensitive drum 1a rotates and the electrostatic latent image
formed on the photosensitive drum 1a reaches the developing roller
4a, toner having a negative polarity is attached to the
electrostatic latent image to visualize the image, and a toner
image of a first color (such as yellow (Y)) is formed on the
photosensitive drum 1a. The other stations (the process cartridges
9b to 9d) corresponding to other colors (magenta (M), cyan (C), and
black (K)) operate similarly. Write signals from a controller (not
shown) are delayed according to the timings corresponding to the
distances between the primary transfer positions of each of the
colors, and the electrostatic latent images formed by scanning
beams 12 from exposing units 11 are formed on each of the
photosensitive drums 1a to 1d. A DC high voltage of an opposite
polarity as toner is applied to each of the primary transfer
rollers 10a to 10d. Thereby, the toner images on the photosensitive
drums 1a to 1d are sequentially transferred to the intermediate
transfer belt 13 (hereinafter referred to as primary transfer), and
a multilayer toner image is formed on the intermediate transfer
belt 13.
[0037] Thereafter, at a matched timing with the creation of the
toner image, a sheet P serving as a recording material supported on
a cassette 16 is fed, or picked up, by a sheet feed roller 17
driven to rotate by a sheet feed solenoid (not shown). The sheet P
being fed is conveyed by a conveyance roller (not shown) to a
registration roller 18. The sheet P is conveyed to a transfer nip
portion, which is a contact portion between the intermediate
transfer belt 13 and a secondary transfer roller 25, by the
registration roller 18 in synchronization with the toner image on
the intermediate transfer belt 13. A voltage having an opposite
polarity as toner is applied to the secondary transfer roller 25
from a secondary transfer high-voltage power supply 26, and a
multilayer toner image of four colors borne on the intermediate
transfer belt 13 is transferred collectively to the sheet P, that
is, on the recording material (hereinafter referred to as secondary
transfer). Meanwhile, toner remaining on the intermediate transfer
belt 13 after the secondary transfer is cleaned by a cleaning unit
27. The sheet P to which secondary transfer has been completed is
conveyed to a fixing unit 50, and the sheet P to which the toner
image has been fixed is discharged onto a discharge tray 30 as a
product having an image printed or copied thereto. A fixing film
51, a nip forming member 52, a pressure roller 53, and a heater 40
of the fixing unit 50 will be described below
Control Block Diagram of Image Forming Apparatus
[0038] FIG. 2 is a block diagram illustrating a configuration of a
control unit of the image forming apparatus, and a printing
operation of the image forming apparatus will be described with
reference to the drawing. A PC 110 serving as a host computer
transmits a print command containing image data and print
information of a print image to a video controller 91 arranged in
the image forming apparatus.
[0039] The video controller 91 converts the image data received
from the PC 110 into exposure data, transfers the exposure data to
an exposure control apparatus 93 within an engine controller 92,
and transmits a print command to a CPU 94. The exposure control
apparatus 93 is controlled by the CPU 94 and controls an exposing
unit 11 that turns a laser light on and off according to the
exposure data. The CPU 94 seizing as a control unit starts an image
forming operation when a print command is received from the video
controller 91.
[0040] The CPU 94 and a memory 95 are installed in the engine
controller 92. The CPU 94 operates according to a program stored in
advance in the memory 95. Further, the CPU 94 includes a timer for
measuring time, and the memory 95 stores various information for
controlling the fixing unit 50 described below. A high-voltage
power supply 96 is composed of the charging high-voltage power
supply 20, the developing high-voltage power supply 21, the primary
transfer high-voltage power supply 22, and the secondary transfer
high-voltage power supply 26 described earlier. A fixing power
control apparatus 97 includes a bidirectional thyristor
(hereinafter referred to as triac) 56 serving as a supply control
unit, and a heating element switching apparatus 552 (refer to FIG.
11) serving as a switching unit for exclusively selecting a heating
element to which power is supplied. The fixing power control
apparatus 97 selects the healing element to which power is suppled
in the fixing unit 50 and determines electric power to be supplied
to the selected heating element.
[0041] A driving device 98 includes a main motor 99 and a fixing
motor 100. Further, a sensor 101 includes a fixing temperature
sensor 60 which is a temperature detection unit for detecting
temperature of the fixing unit 50, a sheet width sensor 102 for
detecting a width of the sheet P, a voltmeter 58, and an ammeter
59, and a detection result of the sensor 101 is transmitted to the
CPU 94. The CPU 94 acquires a detection result of the sensor 101
within the image forming apparatus, and based on the detection
result, controls the exposing unit 11, the high-voltage power
supply 96, the fixing power control apparatus 97, and the driving
device 98. Thereby, the CPU 94 forms the electrostatic latent
image, transfers the developed toner image to the sheet P, and
fixes the transferred toner image to the sheet P, and performs
control of an image forming process in which the image data
received from the PC 110 is printed as toner image on the sheet P.
The image forming apparatus is not limited to the image forming
apparatus having the configuration illustrated in FIG. 1, and it
can be an image forming apparatus having different configuration
and equipped with the fixing unit 50 having the heater 40 described
below and capable of printing images on sheets P having different
widths.
Configuration of Fixing Unit
[0042] FIG. 3A and 3B illustrate a configuration of the fixing unit
50 used in the image forming apparatus according to the present
embodiment. FIG. 3A is a perspective view illustrating a
configuration of the fixing unit 50, and FIG. 3B is a
cross-sectional view in which the fixing unit 50 illustrated in
FIG. 3A is cut at a center in a longitudinal direction thereof.
[0043] The fixing unit 50 is composed of the tubular fixing film
51, the pressure roller 53 that forms the fixing nip portion N
together with the fixing film 51, the heater 40 for heating the
fixing film 51, the nip forming member 52 for holding the heater
40, and a stay 55 for improving strength (stiffness) of the unit in
a longitudinal direction.
[0044] The fixing film 51 includes a polyimide substrate having a
film thickness of 50 .mu.m, a silicon rubber layer having a film
thickness of 200 .mu.m formed thereon, and a perfluoroalkoxy alkane
(PFA) release layer having a film thickness of 20 .mu.m formed
thereon. The pressure roller 53 includes a core metal made of free
machining steel (e.g., SUM grade in Japanese Industrial Standards)
and having an outer diameter of 13 mm, a silicon rubber elastic
layer having a film thickness of 3.5 mm, and a PFA release layer
having a film thickness of 40 .mu.m formed thereon. By rotating the
pressure roller 53 by a driving source (not shown), the fixing film
51 receives drive of the pressure roller 53 and is driven to
rotate. The heater 40 serving as a heating member is arranged in an
interior space of the fixing film 51 and retained by the nip
forming member 52 so that an inner circumference surface of the
fixing film 51 is in contact with a surface of the heater 40. Both
ends of the stay 55 press the nip forming member 52, and the
pressing force thereof is applied via the nip forming member 52 and
the fixing film 51 to the pressure roller 53. Thereby, the fixing
nip portion N is formed by the outer circumference surface of the
fixing film 51 and the pressure roller 53 being in pressure contact
with each other, and the fixing film 51 is nipped by the pressure
roller 53 and the heater 40. The sheet P is fed to the fixing nip
portion N from the illustrated sheet conveyance direction. The nip
forming member 52 is required to have stiffness, heat resistance,
and heat insulation property, and it is formed of a liquid crystal
polymer.
[0045] The fixing temperature sensor 60, which according to the
present embodiment is a thermistor, serving as a temperature
detection unit, and a thermo-switch (thermal switch, not shown)
serving as a safety element are arranged in contact with a rear
surface, which is opposite from the side facing the fixing film 51,
of the heater 40 at a center portion of the rear surface in the
longitudinal direction. The fixing temperature sensor 60 according
to the present embodiment is a chip resistor-type thermistor
(hereinafter referred to as a thermistor 60). The CPU 94 described
above detects a resistance value of the thermistor 60 and performs
a temperature control of the heater 40 based on a detection result
of the resistance value. Further, the thermistor 60 is capable of
detecting excessive temperature rise. Thermistors are arranged on
both longitudinal end portions of the heater 40, which are capable
of detecting a heater temperature of the heater 40 at both
longitudinal end portions. The thermo-switch is a bimetal
thermo-switch, the heater 40 and the thermo-switch are electrically
connected, and in a case where the thermo-switch detects the
excessive temperature rise of the heater 40, the bimetal in the
interior of the thermo-switch operates and power supply to the
heater 40 is cut off.
Heater Configuration
[0046] FIG. 4A is an explanatory view of a configuration of the
heater 40 according to the present embodiment. In FIG. 4A, an upper
right view is a top view illustrating the heater 40 from the
pressure roller 53 side, and the left view is a cross-sectional
view taken at a longitudinal center portion of the heater 40
illustrated on the right view. The lower view is a cross-sectional
view taken at a center portion in a short-length direction of the
heater 40 illustrated on the upper right view.
[0047] The heater 40 adopts a configuration in which heating
elements 42a and 42b mainly composed of silver and palladium, a
conductive path 43 having a lower resistance value than the heating
elements 42a and 42b, and power supply contacts 44a and 44b are
formed on a plate-shaped ceramic substrate 41 formed of alumina,
for example. Areas other than the contacts 44a and 44b are coaled
with an insulative glass 45. When a voltage is applied between the
power supply contacts 44a and 44b, the heating elements 42a and 42b
on the ceramic substrate 41 generate heat. The dimensions of the
ceramic substrate 41 are thickness t=1 mm, width w=7.0 mm, and
length 1=280 mm. The heating elements 42a and 42b have the same
longitudinal length of 222 mm and are arranged in parallel in a
short-length direction of the ceramic substrate 41. A resistance
value of each of the heating elements 42a and 42b is 21.OMEGA., and
the heating elements 42a and 42b are connected in parallel, so that
a synthetic resistance value of the two heating elements 42a and
42b is 10.5.OMEGA.. As described above, the heating elements 42a
and 42b and the conductive path 43 are coated with the glass 45, so
that insulation is retained. The thermistor 60 that detects the
temperature of the heater 40 via the ceramic substrate 41 is
arranged at the longitudinal center portion of the ceramic
substrate 41. The CPU 94 controls electric power to be supplied to
the heating elements 42a and 42b based on the detection result of
temperature of the heater 40 with the thermistor 60.
[0048] FIG. 4B is a schematic diagram illustrating a power supply
path for supplying power to the heater 40 according to the present
embodiment. As illustrated in FIG. 4B, power is supplied from an AC
power supply 57 (denoted by AC in the drawing) via the power supply
contacts 44a and 44b to the heating elements 42a and 42b of the
heater 40. Further, the voltmeter 58 (denoted by V in the drawing)
serving as a voltage detection unit for measuring a voltage applied
to the heating elements 42a and 42b and the ammeter 59 (denoted by
A in the drawing) serving as a current detection unit for measuring
a current value flowing to the heating elements 42a and 42b are
arranged in the power supply path. A triac 56 serving as a switch
connects and disconnects a power supply path from the AC power
supply 57 to the heating elements 42a and 42b. The CPU 94 performs
PI control using a temperature information of the heater 40
detected by the thermistor 60 so that the fixing nip portion N is
maintained at a predetermined temperature, and calculates a ratio,
i.e., duty, of on/off time of the triac 56. The CPU 94 controls the
triac 56 based on the calculated duty.
[0049] The present embodiment can shorten a cooling time of the
pressure roller 53 according to the temperature of the non-sheet
passing portion after a small-size sheet P is passed through by
calculating the temperature of the fixing film 51 serving as the
fixing member highly accurately. Further, the present embodiment
can reduce an occurrence of a hot offset when the large-size sheet
P is passed through after the small-size sheet P is passed through.
Therefore, according to the present embodiment, the accumulated
electrical energy supplied to the non-sheet-passing portion of the
heater 40 is calculated, and the temperature of the
non-sheet-passing portion of the fixing film 51 is calculated based
on the calculated accumulated electrical energy. By calculating the
temperature of the non-sheet-passing portion of the fixing film 51
accurately, the cooling time of the pressure roller 53 after the
small-size sheet P had passed through can be set as short as
possible. In the following description, examples of method for
calculating the temperature of the fixing member of the present
embodiment will be described.
Sheet-Passing Portion of Heater, and Electric Power Supplied to
Non-Sheet-Passing Portion
[0050] FIG. 5 is a view illustrating a positional relationship
between the heater 40 and the small-size sheet P (denoted as
small-size sheet in the drawing) with reference to FIG. 4B. In FIG.
5, a center in a width direction of the small-size sheet P is set
to pass through a center of the longitudinal direction (right-left
direction in the drawing) of the heating elements 42a and 42b of
the heater 40. In the heating elements 42a and 42b illustrated in
FIG. 5, an area of a sheet-passing portion through which the sheet
P passes is denoted by area A, and one of the non-sheet-passing
portions on either side of area A where the sheet P does not pass
through is denoted by area B (non-sheet-passing portion on left
side of drawing) and the other non-sheet-passing portion is denoted
by area C (non-sheet-passing portion on right side of drawing).
Further, a length in a longitudinal direction of the heating
elements 42a and 42b of the heater 40 is denoted by H, a sheet
width, i.e., length in a width direction, of the small-size sheet P
is denoted by ha, a width in the longitudinal direction of area B
serving as the non-sheet-passing portion is denoted by hb, and a
width in the longitudinal direction of area C is denoted by hc. As
described above, the sheet P is passed through the center in the
longitudinal direction of the heating elements 42a and 42b of the
heater 40, so that a width hb of area B and a width hc of area C
have the same length. The sheet width ha can be determined based on
a sheet size information of the sheet P included in a print
information transmitted from the PC 110, or the sheet width ha of
the sheet P can be determined based on the detection result of the
sheet width sensor 102 equipped in the image forming apparatus.
[0051] Further according to the present embodiment, the electric
power supplied to the heating elements 42a and 42b of the heater 40
is calculated based on a voltage information of a voltage applied
to the heating elements 42a and 42b measured by the voltmeter 58
and a current information of a current flown to the heating
elements 42a and 42b measured by the ammeter 59. The electric power
supplied from the AC power supply 57 to the heating elements 42a
and 42b of the heater 40 is denoted by WS, the electric power
supplied to area A which is the sheet-passing portion of the
heating elements 42 and 42b is denoted by WSa, and electric power
supplied to area B and area C which are non-sheet-passing portions
is respectively denoted by WSb and WSc. The electric power WS can
be calculated by a following calculation formula,
WS=WSa+WSb+WSc.
The electric power WSa of area A serving as a sheet-passing area
can be calculated by a following calculation formula,
WSa=WS.times.ha/H.
Further, the electric power WSb of area B being a non-sheet-passing
portion can be calculated by a following calculation formula,
WSb=WS.times.hb/H.
Similarly, the electric power WSc of area C being the
non-sheet-passing portion can be calculated by a following
calculation formula,
WSc=WS.times.hc/H.
The area widths hb and hc have the same length that can be
calculated by a following calculation formula,
hb=hc=(H-ha)/2.
[0052] According to the present embodiment, the electric power
supplied to the non-sheet-passing portion of the heating element of
the heater 40 is accumulated or integrated, and a risen temperature
of the non-sheet-passing portion of the fixing member (hereinafter
referred to as a risen temperature value) is calculated based on
the accumulated value or an integral of electric power, i.e., an
amount measured with a unit of Ws (watt-second) or J (joule). Such
accumulated value is hereinafter referred to as an accumulated
electrical energy. An accumulated electrical energy supplied to the
heater 40 from the AC power supply 57 is denoted by IWS, an
accumulated electrical energy supplied to area B of the
non-sheet-passing portion is denoted by IWSb, and an accumulated
electrical energy of area C of the non-sheet-passing portion is
denoted by IWSc. In the present embodiment, the area widths hb and
hc of areas B and C have the same length, so that the electrical
energy supplied to area B and the electrical energy supplied to
area C are the same. Therefore, the accumulated electrical energy
at area B is calculated, the calculation of risen temperature value
of area B is described, and the description of area C is
omitted.
Risen Temperature Value of Non-Sheet-Passing Portion of Fixing
Member and Transition of Accumulated Electrical Energy
[0053] First, three types of sheets having different sheet widths
were prepared to perform a continuous sheet passing test and to
obtain a risen temperature value (maximum value) of the
non-sheet-passing portion of the fixing member and an accumulated
electrical energy IWSb of the non-sheet-passing portion at that
time, to confirm whether there is a correlation between the
accumulated electrical energy IWSb of area B and the risen
temperature value of the non-sheet-passing portion. The
sheet-passing conditions of the continuous sheet passing test are
as follows. The sheet width ha of the three types of sheets L, M,
and N were each 210 mm, 205 mm, and 200 mm, and the lengths in the
conveyance direction and grammage of the sheets L, M, and N were
each 297 mm and 128 g/m.sup.2. In the continuous sheet passing
test, temperature control was executed so that a detection
temperature of the thermistor 60 arranged in contact with the
heater 40 is maintained at 200.degree. C., the conveyance speed of
sheets was set to 200 mm/s, and the feed interval of the sheets was
set to 0.2 s. The fixing member mentioned here is the fixing film
51 of the fixing unit 50.
[0054] FIG. 6A is a graph illustrating a transition of risen
temperature value of surface temperature of the non-sheet-passing
portion area of the fixing film 51 in a state where sheets L, M,
and N are passed continuously through the fixing nip portion N of
the fixing unit 50. In FIG. 6A, a vertical axis indicates a risen
temperature value (unit: .degree. C.) of the surface temperature of
the non-sheet-passing portion of the fixing film 51, and a
horizontal axis indicates time (unit: s). Further, a solid line in
the graph shows a temperature variation when sheet L is subjected
to continuous-sheet-passing operation, a two-dot chain line in the
graph shows the temperature variation when sheet M is subjected to
continuous-sheet-passing operation, and a dashed line in the graph
shows the temperature, variation when sheet N is subjected to
continuous-sheet-passing operation.
[0055] In the drawing, points indicated by black dots show the time
when the risen temperature value of the non-sheet-passing portion
of the fixing film 51 has reached 200.degree. C. when the sheets L,
M, and N were subjected to continuous-sheet-passing operation. In
FIG. 6A the time T.sub.L200 at which the risen temperature value of
the non-sheet-passing portion of the fixing film 51 had reached
200.degree. C. when sheet L was passed through was 26 s. Similarly,
the time T.sub.M200 and time T.sub.N200 at which the risen
temperature value of the non-sheet-passing portion of the fixing
film 51 had reached 200.degree. C. when sheet M and sheet N were
passed through were 17 s and 12 s, respectively. As illustrated in
FIG. 6A, the sheet N having the smallest sheet width had the
fastest risen temperature speed of the fixing film 51, and the
risen temperature value of the fixing film 51 was saturated at the
highest temperature among the three types of sheets.
[0056] FIG. 6A is a graph illustrating a transition of accumulated
electrical energy IWSb in area B of the non-sheet-passing portion
of the heating elements 42a and 42b in a state were sheets L, M,
and N are continuously passed through the fixing nip portion N of
the fixing unit 50. In FIG. 6B, the vertical axis shows an
accumulated electrical energy IWSb (unit: Ws) supplied to area B
serving as the non-sheet-passing portion of the heating elements
42a and 42b, and the horizontal axis shows time (unit: s). The
solid line in the graph shows a change in the accumulated
electrical energy IWSb When the sheets L were subjected to
continuous-sheet-passing operation, the two-dot chain line in the
graph shows the change in the accumulated electrical energy IWSb
when the sheets M were subjected to continuous-sheet-passing
operation, and the dashed line in the graph shows the change in the
accumulated electrical energy IWSb when the sheets N were subjected
to continuous-sheet-passing operation. As described above, the
electric power WSb at area B of the non-sheet-passing portion can
be calculated by a calculation formula of WSb=WS.times.hb/H. The
accumulated electrical energy IWSb at area B can be calculated by
accumulating the calculated electric power WSb.
[0057] As illustrated in FIG. 6A, the times at which the risen
temperature value of the non-sheet-passing portion of the fixing
film 51 had reached 200.degree. C. when each of the sheets L, M,
and N were subjected to continuous-sheet-passing operation were 26
s, 17 s, and 12 s, respectively. In FIG. 6B, the accumulated
electrical energy IWSb at area B when 26 s, 17 s, and 12 s had
respectively elapsed when sheets L, M, and N had been subjected to
continuous-sheet-passing operation were 220 (Ws), 220 (Ws), and 215
(Ws), respectively, for sheets L, M, and N. That is, the
accumulated electrical energies IWSb supplied to area B of the
non-sheet-passing portion of the heating elements 42a and 42b when
the sheets L, M, and N were subjected to continuous-sheet-passing
operation until the surface temperature of the area of the
non-sheet-passing portion of the fixing film 51 had reached
200.degree. C. were approximately of the same value.
[0058] Further, the above-mentioned continuous sheet passing test
was also performed regarding the correlation of the accumulated
electrical energy IWSb supplied to area B of the non-sheet-passing
portion of the heating elements 42a and 42b of cases where the
surface temperatures of the non-sheet-passing portion area of the
fixing film 51 were 190.degree. C. and 180.degree. C.,
respectively, to confirm whether correlation exists. As illustrated
in FIG. 6A, the time at which the risen temperature value of the
non-sheet-passing portion of the fixing film 51 had reached
190.degree. C. when sheets L, M, and N were each subjected to
continuous-sheet-passing operation were 19 s, 12 s, and 9 s,
respectively. In FIG. 6B, the accumulated electrical energies IWSb
at area B when 19 s, 12 s, and 9 s had elapsed after performing
continuous-sheet-passing operation of sheet L, M, and N,
respectively, were 165 (Ws), 170 (Ws), and 170 (Ws) for sheets L, M
and N, respectively. Further, as illustrated in FIG. 6A, the times
at which the risen temperature value of the non-sheet-passing
portion of the fixing film 51 had reached 130.degree. C. when
sheets L, M, and N had been subjected to continuous-sheet-passing
operation were 14 s, 9 s, and 6 s, respectively. In FIG. 6B, the
accumulated electrical energies IWSb at area B when 14 s, 9 s, and
6 s had elapsed after performing continuous-sheet-passing operation
of sheets L, M, and N, respectively, were 130 (Ws), 135 (Ws), and
130 (Ws) for sheets L, M, and N, respectively. As a result, even in
a case where the surface temperatures of the area corresponding to
the non-sheet-passing portion of the fixing film 51 were
190.degree. C. and 130.degree. C., it was confirmed that there is a
strong correlation with the accumulated electrical energy IWSb
supplied to area B of the non-sheet-passing portion of the heating
elements 42a and 42b.
[0059] FIG. 7A is a graph showing a relationship between a risen
temperature value of the non-sheet-passing portion of the fixing
film 51 and an accumulated electrical energy IWSb supplied to the
non-sheet-passing portion of the heating elements 42a and 42b based
on the result of the continuous sheet passing test mentioned above.
A vertical axis (Y axis) shows a risen temperature value (unit:
.degree. C.) of the non-sheet-passing portion of the fixing film
51, and a horizontal axis (X axis) shows an accumulated electrical
energy (unit: Ws) supplied to area B of the non-sheet-passing
portion of the heating elements 42a and 42b. The graph of FIG. 7A
shows a straight line indicating an approximation that passes
points plotting the accumulated electrical energy IWSb supplied to
the non-sheet-passing portion of the heating elements 42a and 42b
when the risen temperature value of the non-sheet-passing portion
of the fixing film 51 were 180.degree. C., 190.degree. C., and
200.degree. C. If the expression shown in the straight line of FIG.
7A is defined as relational expression 1 (first calculation
formula), the relational expression 1 is represented by
Y=0.23X+150. Alternatively, by creating a table associating the
accumulated electrical energy IWSb supplied to the
non-sheet-passing portion of the heating elements 42a and 42b and
the risen temperature value of the non-sheet-passing portion of the
fixing film 51 using the relational expression 1, the risen
temperature value of the non-sheet-passing portion of the fixing
film 51 can be calculated based on the accumulated electrical
energy IWSb.
[0060] Further, according to the graph showing the risen
temperature value of the non-sheet-passing portion of the fixing
film 51 illustrated in FIG. 6A, it can be recognized that the risen
temperature values of the non-sheet-passing portion of the fixing
film 51 corresponding to sheets L, M, and N are each saturated to
converge to a certain temperature. Specifically, the risen
temperature values of the non-sheet-passing portion of the fixing
film 51 of sheets L, M, and N are each saturated at 210.degree. C.,
230.degree. C., and 255.degree. C., respectively. In the document,
this temperature is defined as a risen temperature saturation value
or a saturation temperature. Next, a method for calculating the
risen temperature saturation value will be described.
[0061] FIG. 6B is a graph showing a transition of the accumulated
electrical energy IWSb at area B of the non-sheet-passing portion
of the heating elements 42a and 42b When the sheets L, M, and N
were subjected to continuous-sheet-passing operation. A ratio, or
change rate, of variation of Y to variation of X, that is, an
inclination a of the linear approximation expression, is calculated
in a state where the graphs of sheets L, M, and N illustrated in
FIG. 6B are shown by a linear approximation expression with the
accumulated electrical energy shown in the vertical axis denoted by
Y and the time shown in the horizontal axis denoted by X. The
inclinations a according to sheets L, M, and N were 7.2, 10.2, and
13.3, respectively. The inclination of the graph where the elapsed
time of passing of the sheets L, M, and N through the fixing nip
portion N of the fixing unit 50 is 4 s or longer is calculated.
Therefore, a linear expression indicating the accumulated
electrical energies y of the sheets L, M, and N illustrated in FIG.
6B are each approximated by y=7.2 x, y=10.2 x, and y=13.3 x.
[0062] FIG. 7B is a graph showing a relationship between the risen
temperature saturation value of the non-sheet-passing portion of
the fixing film 51 based on the continuous sheet passing test
result described above and the inclination a calculated from the
graph of FIG. 6B. A vertical axis (Y axis) of FIG. 7B shows the
risen temperature saturation value (unit: .degree. C.) of the
non-sheet-passing portion of the fixing film 51, and a horizontal
axis (X axis) shows the inclination of the graph shown in FIG. 6B,
that is, the variation of the accumulated electrical energy IWSb in
area B of the non-sheet-passing portion of the sheet-passing time.
The graph of FIG. 7B shows a straight line indicating an
approximation that passes points plotting inclination a calculated
by the graph of FIG. 6B for sheets L, M, and N in a state where the
risen temperature saturation values are 210.degree. C., 230.degree.
C., and 255.degree. C., and it can be confirmed that there is a
correlation between inclination .alpha. and the risen temperature
saturation value. If the expression showing the relationship
between the inclination .alpha. (X axis) and the risen temperature
saturation value (Y axis) indicated in FIG. 7B is defined as a
relational expression 2 (second calculation formula), the
relational expression 2 can be represented by Y=7.4X+156.
Relationship between Accumulated Electrical Energy of
Non-Sheet-Passing Portion of Heater and Risen Temperature Value of
Non-Sheet-Passing Portion of Fixing Film
[0063] Next, a method for calculating a relational expression 3
considering the risen temperature saturation value mentioned
earlier will he described based on the relational expression 1
indicating the relationship between the accumulated electrical
energy IWSb at area B of the non-sheet-passing portion of the
heating elements 42a and 42b of the heater 40 illustrated in FIG.
7A and the risen temperature value of the non-sheet-passing portion
of the fixing film 51. In the relational expression 1 illustrated
in FIG. 7A, if the risen temperature value of the non-sheet-passing
portion calculated by the relational expression 1 is higher than
the above-mentioned risen temperature saturation value, a
relational expression 3 for substituting the value of temperature
rise in non-sheet-passing portion calculated by the relational
expression 1 by the risen temperature saturation value is created.
The example of a sheet P having a sheet width of 207 mm will be
described as a specific example. The inclination .alpha. of a state
in which the sheet P having a sheet width of 207 mm is passed
through is 11. By substituting inclination .alpha.=11 (that is,
X=11) to the relational expression 2 mentioned above, the risen
temperature saturation value Y is calculated as 238.degree. C.
(.apprxeq.7.4 [.degree. C.].times.11+156 [.degree. C.]). Further,
in the relational expression 1, the value of temperature rise in
non-sheet-passing portion corresponding to the accumulated
electrical energy in which the value of temperature rise in
non-sheet-passing portion becomes higher than 238.degree. C. is all
substituted by 238.degree. C. which is the risen temperature
saturation value. Thereby, the relationship between the final
accumulated electrical energy of the non-sheet-passing portion of
the heating elements 42a and 42b and the risen temperature value of
the non-sheet-passing portion of the fixing film 51 can be shown by
the graph illustrated in FIG. 8.
[0064] FIG. 8 is a graph showing a relationship between the
accumulated electrical energy supplied to the non-sheet-passing
portion of the heating elements 42a and 42b and the risen
temperature value of the non-sheet-passing portion of the fixing
film 51. In FIG. 8, a vertical axis (Y axis) shows a risen
temperature value (unit: .degree. C.) of the non-sheet-passing
portion of the fixing film 51, and a horizontal axis (X axis) shows
an accumulated electrical energy supplied to the non-sheet-passing
portion of the heating elements 42a and 42b. When the accumulated
electrical energy of the non-sheet-passing portion is represented
by X and the risen temperature value of the non-sheet-passing
portion is represented by Y, the relational expression 3
representing the graph illustrated in FIG. 8 calculates the value
of Y using Y=0.23 X+150 according to the relational expression 1 in
a case where the value of X is 0 to 383, and sets value Y to Y=238
in a case where the value of X exceeds 383. Based on the relational
expression 3 and the accumulated electrical energy of the
non-sheet-passing portion of the heating elements 42a and 42b after
printing is ended, the risen temperature value of the
non-sheet-passing portion of the fixing film 51 after the printing
is ended can be calculated.
Cooling Time of Fixing Unit according to Risen Temperature Value of
Non-Sheet-Passing Portion
[0065] Next, a cooling time with respect to the risen temperature
value of the non-sheet-passing portion of the fixing film 51 will
be described. The cooling time is a time for lowering a temperature
of a non-sheet-passing portion in a high temperature state of the
fixing film 51 of the fixing unit 50 heated by passing a small-size
sheet with a narrow sheet width to a predetermined temperature,
that is, period of time of execution of the operation of heat
leveling for leveling a heat distribution in the nip portion.
Further, the predetermined temperature refers to a temperature in
which hot offset does not occur even if the sheet width of the
sheet P to be printed next is wider than the sheet width of the
sheet P to which printing has been performed immediately before. By
lowering the temperature of the non-sheet-passing portion of the
fixing film 51 to a predetermined temperature for heat leveling,
the occurrence of a hot offset can be suppressed even if a
large-size paper having a wide width is passed through after the
small-size sheet is passed through. In the present embodiment, the
risen temperature value of the non-sheet-passing portion of the
fixing film 51 after passing through the small-size sheet is
calculated, and according to the calculated risen temperature
value, the cooling time for lowering the temperature of the
non-sheet-passing portion of the fixing film 51 is determined. The
cooling time is determined to be longer if the risen temperature
value of the non-sheet-passing portion of the fixing film 51 is
high and shorter if low. During the cooling time, the pressure
roller 53 of the fixing unit 50 can be rotated continuously or can
be stopped without being rotated.
Control Sequence of Cooling of Fixing Unit
[0066] FIG. 9 is a flowchart showing a control sequence of cooling
for lowering the risen temperature value of the non-sheet-passing
portion of the fixing film 51 of the fixing unit 50 mentioned
above. The processing illustrated in FIG. 9 is started when
printing of the sheet P is performed, and it is executed by the CPU
94. The CPU 94 performs temperature control of the fixing film 51
of the fixing unit 50 by controlling power supply to the heating
elements 42a and 42b of the heater 40, but it is assumed to be
executed by a different processing as the processing illustrated in
the flowchart of FIG. 9. Further, it is assumed that the length
information in the longitudinal direction of the heating elements
42a and 42b and the above-mentioned relational expressions 1 and 2
are stored in advance in the memory 95. Further, it is assumed that
a table associating the risen temperature value of the
non-sheet-passing portion of the fixing film 51 and a cooling time
for lowering the temperature of the non-sheet-passing portion of
the fixing film 51 to the predetermined temperature is stored in
the memory 95.
[0067] In the image forming apparatus, when a print command is
received from the PC 110, the video controller 91 transmits a print
command including the information of the sheet P to the CPU 94, and
the CPU 94 having received the print command from the video
controller 91 starts the printing operation of the sheet P. The
print job based on the print command from the PC 110 is assumed to
be the print job using the sheet P having the same sheet size.
[0068] In step (hereinafter abbreviated as S) 100, the CPU 94
acquires a sheet width ha based on information of the sheet P
contained in the print command received from the video controller
91 and acquires a length information H in the longitudinal
direction of the heating elements 42a and 42b from the memory 95.
In S101, the CPU 94 sets the accumulated electrical energy IWSb in
area B of the non-sheet-passing portion of the heating elements 42a
and 42b to 0.
[0069] In S102, the CPU 94 acquires a voltage information applied
to the heating elements 42a and 42b measured by the voltmeter 58
and a current information flowing to the heating elements 42a and
42b measured by the ammeter 59. In S103, the CPU 94 calculates the
electric power WS (=voltage.times.current) being supplied to the
heating elements 42a and 42b based on the voltage information and
the current information acquired in S102. Then, the CPU 94
calculates the electric power WSb of the non-sheet-passing portion
described earlier using the calculated electric power WS, the sheet
width ha of the sheet P, and the longitudinal length of area B of
the non-sheet-passing portion of the healing elements 42a and 42b
(heating element length H--sheet width ha)/2. Further, the CPU 94
adds the calculated electric power WSb to the value of the
accumulated electrical energy IWSb of area B of the
non-sheet-passing portion of the healing elements 42a and 42b,
updates the value of the accumulated electrical energy IWSb, and
saves the updated accumulated electrical energy IWSb in the memory
95. In S104, the CPU 94 determines whether the print job has ended,
wherein if it is determined that the print job has not ended, the
procedure returns to S102, and if it is determined that the print
job has ended, the procedure advances to S105.
[0070] In S105, the CPU 94 reads the accumulated electrical energy
IWSb stored in the memory 95 each time update is performed and
calculates the inclination a indicating the variation of the
accumulated electrical energy IWSb accompanying time transition. In
S106, the CPU 94 reads the relational expression 2 described
earlier from the memory 95 and substitutes the inclination a
calculated in S105 to the relational expression 2 being read, to
thereby calculate the risen temperature saturation value of the
non-sheet-passing portion of the fixing film 51 with respect to the
sheet P.
[0071] In S107, the CPU 94 uses the risen temperature saturation
value calculated in S106 and relational expression 1 (accumulated
electrical energy of non-sheet-passing portion and temperature rise
in non-sheet-passing portion) read from the memory 95 to generate
the above-mentioned relational expression 3 in which all the
temperature rise values in non-sheet-passing portion higher than
the risen temperature saturation value are substituted by the risen
temperature saturation value. In S108, the CPU 94 reads the
accumulated electrical energy IWSb when the print job is ended
stored in the memory 95, and the accumulated electrical energy IWSb
being read is substituted in the relational expression 3 generated
in S107, and the risen temperature value of the non-sheet-passing
portion of the fixing film 51 when the print job is ended is
calculated. In other words, the CPU 94 serves as a temperature
calculation unit configured to calculate a temperature of the film
in the second area (non-sheet-passing area).
[0072] In S109, the CPU 94 acquires the cooling time corresponding
to the risen temperature value of the non-sheet-passing portion of
the fixing film 51 calculated in S108 from the table associating
the risen temperature value of the non-sheet-passing portion of the
fixing film 51 with the cooling time of the fixing film 51 stored
in the memory 95. In S110, the CPU 94 stops the pressure roller 53
of the fixing unit 50, and resets and starts a timer. In S111, the
CPU 94 refers to the timer, and determines whether a timer value
has passed the cooling time. if the CPU 94 determines that the
timer value has not passed the cooling time, the procedure is
returned to S111, and if it is determined that the timer value has
passed the cooling time, the procedure is ended.
[0073] In this example, during the cooling time, the processing of
stopping the rotation of the pressure roller 53 when lowering the
temperature of the non-sheet-passing portion of the fixing film 51
was performed. Alternately, for example, the pressure roller 53 for
lowering the temperature of the non-sheet-passing portion of the
fixing film 51 can be rotated during the cooling time, and the
processing of stopping the rotation of the pressure roller 53 can
be performed after the cooling time had elapsed.
[0074] Further, according to the present embodiment, the print job
of performing printing to sheets P of the same size was taken as an
example. Alternately, in the case of a print job in which printing
is performed to a plurality of sheets P having different sizes, it
is possible to perform the cooling process of the pressure roller
53 when the sheet size is changed, and to perform the printing of
the subsequent sheet P after the cooling process has been
ended.
[0075] As described earlier, according to the present embodiment,
the cooling time of the fixing unit after the small-size sheet had
passed is shortened by accurately calculating the risen temperature
value of the non-sheet-passing portion of the fixing member based
on the accumulated electrical energy of the non-sheet-passing
portion of the heating element and the risen temperature saturation
value of the non-sheet-passing portion. By executing cooling of the
fixing member appropriately according to the temperature of the
fixing member, the occurrence of hot offsets can be reduced even if
a large-size paper is passed through after a small-size paper had
passed through.
[0076] As described above, according to the present embodiment, the
period of rotation of the pressure roller for cooling the fixing
member can be controlled according to the temperature of the
non-sheet-passing portion of the fixing member of the fixing
unit.
Second Embodiment
[0077] The first embodiment illustrated an example of a case where
the electrical energy of the area of the non-sheet-passing portion
of the heating element of the heater is calculated based on the
voltage information measured by the voltmeter and the ammeter and
the current information. The second embodiment illustrates a method
of calculating an electrical energy of an area of a
non-sheet-passing portion of a heating element of a heater in a
fixing unit that is not equipped with a voltmeter and an
ammeter.
Heater Configuration
[0078] FIG. 10A is a schematic diagram illustrating a power supply
path for supplying power to the heater 40 according to the present
embodiment. FIG. 10A differs from FIG. 5 illustrating the first
embodiment in that the voltmeter 58 and the ammeter 59 are not
provided. The other configurations of the image forming apparatus
are similar to the first embodiment, so that by assigning the same
reference numbers as the first embodiment to the same members, the
description thereof is omitted.
[0079] In the present embodiment, the memory 95 stores an
application voltage table associating a temperature difference
between a target temperature of the healer 40 and a temperature of
the heater 40 detected by the thermistor 60 with a voltage to be
applied to the heater 40. Further, the memory 95 also stores a
control signal table associating the voltage to be applied to the
heater 40 with a timing and output interval of outputting a control
signal for turning on the triac 56. The CPU 94 periodically detects
a temperature difference from the target temperature of the heater
40 based on the temperature detection result of the heater 40 by
the thermistor 60, and acquires an application voltage according to
the detected temperature difference from the application voltage
table. Further, the CPU 94 determines an output timing of a control
signal of the triac 56 according to the acquired application
voltage based on the control signal table, and outputs the control
signal to the triac 56 according to the output timing. According to
the present embodiment, the CPU 94 outputs the control signal
according to a half-wave cycle, i.e., every half cycle, of an AC
voltage waveform of the AC power supply 57. When a control signal
is output from the CPU 94, the triac 56 is set to an on state
during the half cycle of the AC voltage waveform, and the AC
voltage from the AC power supply 57 is supplied to the heater
40.
Relationship between AC voltage and Control Signal for Triac
[0080] FIG. 10B is an explanatory view illustrating a relationship
between an AC voltage of the AC power supply 57 and a control
signal for driving the triac 56. In FIG. 10B, the lower drawing
illustrates a control signal of the triac 56 output from the CPU
94, and the triac 56 is turned on for half a cycle of the AC
voltage output from the control signal. The upper drawing
illustrates a waveform of AC voltage (denoted as AC voltage in the
drawing) supplied from the AC power supply 57 to the heater 40, and
AC voltage is supplied to the heater 40 for half a cycle only when
the control signal is output. The hatching in the drawing indicates
a state in which AC voltage is supplied to the heater 40. The AC
power supply 57 has a voltage of 100 V, and a power supply
frequency of 50 Hz, and a combined resistance of the heating
elements 42a and 42b of the heater 40 is 10.5.OMEGA.. Then, a
maximum electric power WS per second supplied to the heater 40 is
WS=V.sup.1/R=100 (V).times.100 (V)/10.5 (.OMEGA.).apprxeq.952 [W].
The power supply frequency 50 Hz has 50 cycles (=100 half waves)
per second, and one half-wave corresponds to 1 (s)/100 (times)=0.01
s. Therefore, the electrical energy supplied to the heater 40 per
one half-wave will be (100) (V).times.100
(V)/10.5(.OMEGA.)).times.0.01 (s)=9.52 [Ws]
[0081] In the present embodiment, the CPU 94 adds the electrical
energy 9.52 [Ws] to the accumulated electrical energy IWS each time
a control signal is output to the triac 56. The accumulated
electrical energy IWSb at area B of the non-sheet-passing portion
of the heater 40 can be calculated by the calculation formula of
accumulated electrical energy IWSb=hb/H.times.IWS described in the
first embodiment. After the calculation of the accumulated
electrical energy of the non-sheet-passing portion of the heater
40, the method for calculating the risen temperature saturation
value of the non-sheet-passing portion, the relational expression
3, and the risen temperature value of the non-sheet-passing portion
are the same as the first embodiment, so that descriptions thereof
will be omitted.
[0082] In the present embodiment, the electrical energy was
calculated assuming that the synthetic resistance value of the
heating elements 42a and 42b is 10.5.OMEGA. and the AC voltage
value of the AC power supply 57 is 100 V. The dispersion of the
resistance value of the heating elements 42a and 42b is as small as
.+-.7%, so that it has little impact on the measurement accuracy of
the electrical energy. Meanwhile, the dispersion of power supply
voltage of the AC power supply 57 varies according to operating
environment, so that it may have some impact on the measurement
accuracy of the electrical energy. Since it is not desirable that
the accumulated electrical energy at the non-sheet-passing portion
of the heater 40 is calculated too low it is desirable that the
power supply voltage of the AC power supply 57 is set to the
maximum assumable voltage value. The information on the resistance
value of the heating elements 42a and 42b and the power supply
voltage of the AC power supply 57 can be stored in advance in the
memory 95, and the CPU 94 can refer to the information when
necessary.
[0083] Further, the flowchart illustrated in FIG. 9 of the first
embodiment is also applicable to the second embodiment. According
to FIG. 9, in the processing of S102, the CPU 94 acquired the
voltage information and the current information measured by the
voltmeter 58 and the ammeter 59, and in the processing of S103, the
acquired voltage information and current information were used to
calculate the electric power and update the accumulated electrical
energy. In the second embodiment, unlike the first embodiment, the
voltmeter 58 and the ammeter 59 are not provided.
[0084] Therefore, in order to apply the flowchart of FIG. 9 to the
second embodiment, the processing of S102 and S103 can be changed
in the following manner. In the processing of S102, the CPU 94
determines whether to output a control signal to the triac 56,
wherein if the control signal is to be output, the procedure
advances to step S103, and if the control signal is not to be
output, the procedure advances to S104. Further, in the processing
of S103, the CPU 94 adds the electrical energy 9.52 [Ws] to be
supplied to area B of the non-sheet-passing portion of the heater
40 during a half-wave cycle of AC voltage to the accumulated
electrical energy IWSb and stores the updated accumulated
electrical energy IWSb in the memory 95.
[0085] Alternately, in the processing of S103, it is possible to
count the number of times the control signal has been output to the
triac 56, and when it is determined in S104 that the print job has
ended, the accumulated electrical energy can be calculated by
multiplying the electrical energy 9.52 [Ws] by the count value.
[0086] As described above, according to the present embodiment, the
accumulated electrical energy of the non-sheet-passing portion is
calculated by accumulating the electrical energy supplied to the
heater 40 per half-wave cycle of the power supply frequency from
the AC power supply 57 every time a control signal to the triac 56
is output. Similarly to the first embodiment, the cooling time of
the fixing unit after a small-size sheet has been passed through by
calculating the risen temperature value of the non-sheet-passing
portion of the fixing member with high accuracy based on the
accumulated electrical energy of the non-sheet-passing portion of
the heating element and the risen temperature saturation value of
the non-sheet-passing portion. By executing cooling of the fixing
member appropriately according to the temperature of the fixing
member, the occurrence of hot offset can be reduced even if a
large-size sheet is passed through after the passing of a
small-size sheet.
[0087] As described above, according to the present embodiment, the
period of rotation of the pressure roller for cooling the fixing
member can be controlled according to the temperature of the
non-sheet-passing portion of the fixing member of the fixing
unit.
Third Embodiment
[0088] According to the heater of the first and second embodiments,
only one kind of heating element was provided. The heater according
to the third embodiment includes a plurality of heating elements,
so the method for controlling the electrical energy supplied to the
non-sheet-passing portion of the heating elements by changing the
usage proportions of the heating elements will be described.
Heater Configuration
[0089] FIG. 11A illustrates a configuration of a heater 54
according to a present embodiment. The heater 54 is formed by
providing, on a heater substrate 549 of Al.sub.2O.sub.3 material
(thickness t=1 mm, width w=6.3 mm, and length 1=280 mm), heating
elements formed of a conductive material mainly composed of silver
and palladium, conduction paths mainly composed of silver, and
contacts for power supply. The width w denotes a length in the
short-length direction of the drawing, and length 1 denotes a
length in the longitudinal direction of the drawing. The heater 54
includes heating elements 541 and 542 having the longest length in
the longitudinal direction, a heating element 543 having the second
longest length in the longitudinal direction, and a healing element
544 having the shortest length in the longitudinal direction. The
dimensions of the heating elements 541 and 542 are thickness t=10
.mu.m, width w=0.7 mm, and length 1=222 mm, corresponding to a
sheet width 210 mm of an A4-size sheet. Further, the dimension of
the heating element 543 is t=10 .mu.m, width w=0.7 mm, and length
1=188 mm, corresponding to a sheet width 182 mm of a B5-size sheet.
The dimensions of the heating element 544 are thickness t=10 .mu.m,
width w=0.7 mm, and length 1=154 mm, corresponding to a sheet width
148.5 mm of an A5-size sheet.
[0090] A first end of each of the heating elements 541 and 542,
i.e., first heating element, is electrically connected to a contact
545 for power supply, and a second end of each of the heating
elements is electrically connected to a contact 546 for power
supply. Further, a first end of the heating element 543, i.e.,
second heating element, is connected to a contact 547 for power
supply, and a second end is electrically connected to the contact
546 for power supply. Then, a first end of the heating element 544,
i.e., second heating element, is connected to the contact 547 for
power supply, and a second end is electrically connected to a
contact 548 for power supply.
[0091] The electric resistance of each of the heating elements 541
and 542 is 21.OMEGA., and the synthetic resistance value of the
heating elements 541 and 542 between the contacts 545 and 546 for
power supply is 10.5.OMEGA.. Further, the resistance value of the
heating element 543 is 24.OMEGA., and the resistance value of the
heating element 544 is 28.OMEGA.. The intervals in the short-length
direction in the drawing between each of the heating elements 541,
542, 543, and 544 is 0.7 mm.
Arrangement of Heating Element
[0092] Next, the arrangement of each of the heating elements 541,
542, 543, and 544 on the heater substrate 549 will be described.
The heating elements 541 and 542 serving as a first heating element
is a heating element that receives the maximum power supply
quantity from the AC power supply 57, and they can heat the fixing
unit 50 to a sheet-passing state in a short time. The heating
elements 541 and 542 can be heated in a short time, but a heating
unevenness of the heater substrate 549 when maximum voltage is
applied thereto is great, so that deformation of the heater
substrate 549 may occur. Therefore, according to the present
embodiment, two heating elements 541 and 542 are arranged in
parallel so as not to have power concentrate to one area. Further,
the heating elements 541 and 542 are arranged symmetrically with
respect to a center of the heater substrate 549 in the short-length
direction, so that the heating unevenness of the heater substrate
549 is reduced.
[0093] Meanwhile, there is only one heating element 543 serving as
a second heating element and there is only one heating element 544
serving as a third heating element so that the increase in size of
the heater 54 can he suppressed. The heating elements 543 and 544
have a short longitudinal length compared to the heating elements
541 and 542, so that they are not suitable from the viewpoint of
leveling heating of the heater substrate 549, so that by setting
the power supply quantity thereto from the AC power supply 57 to a
small value, the heating unevenness of the heater substrate 549 is
reduced.
Control of Power Supply Path
[0094] Next, control of power supply path for supplying power to
each of the heating element will be explained. FIG. 11B is a
schematic diagram illustrating a power supply path for supplying
power from the AC power supply 57 to the heater 54. In FIG. 11B, a
first end of the AC power supply 57 is connected to a first end of
triacs 550 and 551, and a second end thereof is connected to the
contact 546 for power supply of the heater 54 and a changeover
contact relay (hereinafter referred to as a relay 552) serving as
the healing element switching apparatus 552. A second end of the
triac 550 is connected to the contact 545 for power supply of the
heater 54. Meanwhile, a second end of the triac 551 is connected to
the relay 552 and the contact 548 for power supply of the heater
54. The relay 552 serving as a switch includes three contacts,
which are a contact connected to the second end of the triac 551, a
contact connected to the second end of the AC power supply 57, and
a contact connected to the contact 547 for power supply of the
heater 54. The contact connected to the contact 547 of the relay
552 can be connected to the contact connected to the second end of
the triac 551 or the contact connected to the second end of the AC
power supply 57 by a relay control signal output from the CPU
94.
[0095] As illustrated in FIG. 11B, a configuration of the power
supply path according to the present embodiment differs from the
configuration of the power supply path of the first embodiment
illustrated in FIG. 4B in that the number of triacs is changed from
one to two, that the relay 552 is added, and that the voltmeter 58
and the ammeter 59 are eliminated. The other configuration of the
image forming apparatus are similar to the first embodiment, so
that by assigning the same reference numbers to the same members,
the descriptions thereof are omitted.
[0096] When supplying power from the AC power supply 57 to the
heating elements 541 and 542, the CPU 94 outputs a control signal
to the triac 550 to turn the triac 550 on and applies the AC
voltage between the contact 545 and the contact 546 of the heater
54. When supplying power from the AC power supply 57 to the heating
element 543, the CPU 94 outputs a control signal to the triac 551
to turn the triac 551 on and applies the AC voltage between the
contact 547 and the contact 546 of the heater 54. In this state,
the CPU 94 will not output a relay control signal to the relay 552,
so that the contact connected to the contact 547 of the heater 54
and the contact connected to the triac 551 are connected by the
relay 552. When supplying power from the AC power supply 57 to the
heating element 544, the CPU 94 outputs a relay control signal, and
the relay 552 connects the contact connected to the contact 547 of
the heater 54 and the contact connected to the AC power supply 57.
Then, after switching the connection of the relay 552, the CPU 94
outputs a control signal to the triac 551 to turn on the triac 551
and applies the AC voltage between the contact 547 and the contact
548 of the heater 54.
[0097] As mentioned above, the synthetic resistance value of the
heating elements 541 and 542 is 10.5.OMEGA., and the resistance
values of the heating elements 543 and 544 are 24.OMEGA. and
28.OMEGA., respectively. For example, if a maximum voltage capable
of being supplied from the AC power supply 57 is 120 V the maximum
current value at the heating elements 541 and 542 will be 11.43 A,
the maximum current value at the heating element 543 will be 5 A,
and the maximum current value at the heating element 544 will be
4.29 A. The current value suppliable through an AC voltage line for
home is generally 15 A or lower, and if AC voltage is applied
simultaneously to a plurality of heating elements, such as the
heating elements 541 and 542 and the heating element 543, the
current value may exceed 15 A. Therefore, according to the present
embodiment, control is performed so that if AC voltage is to be
applied, or power is to be supplied, to one of the heating
elements, AC voltage from the AC power supply 57 will not be
applied to the other two heating elements. That is, while
outputting a control signal to the triac 550 illustrated in FIG.
11B, the CPU 94 will not output a control signal to the triac 551.
Since the triacs 550 and 551 will not be turned on simultaneously,
the AC voltage from the AC power supply 57 will not be applied to a
plurality of heating elements.
Control of Power Supply to Heater
[0098] Next, a control of power supply to the heater 54 will be
explained. For example, when a B5-size sheet is passed through, the
heating elements 541 and 542, and the heating element 543 having a
longitudinal length approximate the B5-size sheet width, are used
as the heating elements to which power from the AC power supply 57
is supplied. Further, when a A5-size sheet is passed through, the
heating elements 541 and 542, and the heating element 544 having a
longitudinal length approximate the A5-size sheet width, are used
as the heating elements to which power from the AC power supply 57
is supplied.
[0099] The CPU 94 detects the temperature difference from the
target temperature of the heater 54 based on the temperature
detection result of the heater 54 by the thermistor 60, and
acquires the application voltage according to the temperature
difference being ed based on the application voltage table
explained in the second embodiment. Further, the CPU 94 determines
the output timing of the control signal of the triacs 550 and 551
according to the acquired application voltage based on the control
signal table explained in the second embodiment, and outputs a
control signal to either one of the triacs 550 and 551 according to
the output timing. The CPU 94 determines which heating element
should receive power supply by referring to usage proportions of
the heating elements determined in advance. Control of power supply
is performed based on a usage time ratio, so that for example, if
the usage proportion of the heating elements 541 and 542 is 30% and
the usage proportion of the heating element 543 is 70%, power
supply to the heating elements 541 and 542 is performed for 0.3 s,
and power supply to the heating element 543 is performed for 0.7
s.
[0100] There are two states of the fixing unit 50 when a sheet is
passed through, which are a cooled state in which the heater 54 is
not heated, and a warmed state in which the heater 54 is heated. In
a state where the fixing unit 50 is cooled, there is a member that
needs to be heated by applying power supply other than the part
through which the sheet is passed, so that a greater electric power
needs to be applied to the heater 54 to warm, or heat, the entire
heater 54 using the heating elements 541 and 542. Meanwhile, in a
state where the fixing unit 50 is warmed, there is no need to apply
such a high electric power compared to the cooled state, but the
power supply quantity to the heating elements 543 and 544 is small,
as mentioned earlier. Therefore, the usage proportion of the
heating elements 541 and 542 needs to be varied between the cooled
state and the warmed state of the fixing unit 50. That is, the CPU
94 increases the usage proportion of the heating elements 541 and
542 having a greater power supply quantity in a state where the
fixing unit 50 is cooled and increases the usage proportions of the
heating elements 543 and 544 in a state where the fixing unit 50 is
warmed so as to cut down the power supply quantity to the
non-sheet-passing portion of the heater 54.
[0101] Determination of whether the fixing unit 50 is in a cooled
state or a warmed state is performed based on the detection
temperature of the thermistor 60 arranged in contact with the
heater substrate 549. The fixing unit 50 is in a warmed state if
the detection temperature of the thermistor 60 is high. According
to the present embodiment, the detection temperature of the
thermistor 60 is divided into four temperature sections, and the
sections are defined as warm-up levels 1, 2, 3, and 4, wherein the
higher warm-up level indicates that the fixing unit 50 is warmed to
a higher temperature.
[0102] Table 1 is a table indicating the temperature definition of
the warm-up level of the fixing unit 50 and usage proportions of
the heating elements 541, 542, 543, and 544 according to each
warm-up level. In Table 1, a fixing unit warm-up level indicates
warm-up levels 1 to 4, and a thermistor detection temperature shows
the range of detection temperature of the thermistor 60
corresponding to each warm-up level. For example, if the
temperature of the heater 54 detected by the thermistor 60 is lower
than 50.degree. C., the warn-up level of the fixing unit 50 is
defined as level 1. Similarly, if the detection temperature of the
heater 54 detected by the thermistor 60 is 80.degree. C.,
120.degree. C., or 155.degree. C., for example, the warm-up level
is set to level 2, level 3, or level 4, respectively. Further, the
usage proportion (unit: %) of the heating element indicates a usage
proportion (percentage) of the heating element corresponding to the
warm-up level. The usage proportions of heating elements indicated
on the left side shows the usage proportions of the heating
elements 541 and 542 and the heating element 543 used according to
the warm-up level of the fixing unit 50 when a B5-size sheet is
passed through. Meanwhile, the usage proportions of heating
elements indicated on the right sideshows the usage proportions of
the heating elements 541 and 542 and the heating element 544 used
according to the warm-up level of the fixing unit 50 when a B5-size
sheet is passed through. As shown in Table 1, the usage proportions
of the heating elements 541 and 542 is set to be higher if the
warm-up level is lower and the fixing unit 50 is not warmed.
TABLE-US-00001 TABLE 1 USAGE PROPORTION OF USAGE PROPORTION OF
HEATING ELEMENT [%] HEATING ELEMENT [%] FIXING UNIT THERMISTOR
HEATING HEATING HEATING HEATING WARM-UP DETECTION ELEMENTS ELEMENT
ELEMENTS ELEMENT LEVEL TEMPERATURE 541, 542 543 541, 542 544 1
LOWER THAN 50.degree. C. 50 50 50 50 2 50.degree. C. OR HIGHER AND
30 70 30 70 LOWER THAN 100.degree. C. 3 100.degree. C. OR HIGHER
AND 20 80 20 80 LOWER THAN 150.degree. C. 4 150.degree. C. OR
HIGHER 10 90 10 90
Calculation of Power Supply Quantity to Heater
[0103] As shown in Table 1, when a B5-size sheet is passed through,
the heating elements 541 and 542 and the heating element 543 are
used. FIG. 12 is a view illustrating the relationship between a
B5-size sheet and the size of the heating elements 541 and 542 and
the heating element 543. FIG. 12A illustrates a positional
relationship between the heating elements 541 and 542 and the
B5-size sheet, and FIG. 12B illustrates a positional relationship
between the heating element 543 and the B5-size sheet. In FIG. 12A,
the sheet width ha of the B5-size sheet serving as a small-size
sheet is 182 mm. The lengths of the heating elements 541 and 542 in
the longitudinal direction of the drawing are the same, and length
H1 is 222 mm. Further, lengths hb1 and hc1 of the non-sheet-passing
area of the heating elements 541 and 542 through which the B5-size
sheet does not pass are each 20 mm (=(222 [mm]-182 [mm])/2). In
FIG. 12B, a length H2 in the longitudinal direction of the heating
element 543 is 188 mm, and lengths hb1 and hc2 of the
non-sheet-passing area of the heating element 543 where the B5-size
sheet does not pass through are each 3 mm (=(188 [mm]-182
[mm])/2).
[0104] Similarly to the second embodiment, regarding the power
supply quantity of the heater 54 to the heating element, the CPU 94
accumulates the electrical energy based on the number of control
signals output to the triacs 550 and 551. For example, it is
assumed that the synthetic resistance value of the heating elements
541 and 542 is 10.5.OMEGA., the AC voltage of the AC power supply
57 is 100 V, and the power supply frequency is 50 Hz. Then, the
electrical energy per one half-wave of the power supply frequency
(0.01 s) will be (100 [V].times.100 [V]/10.5 |.OMEGA.|).times.0.01
[s]=9.52 [Ws]. Meanwhile, if it is assumed that the resistance
value of the heating element 543 is 24.OMEGA., the AC voltage of
the AC power supply 57 is 100 V, and the power supply frequency is
50 Hz, the electrical energy per one half-wave of the power supply
frequency will be (100 [V].times.100 [V]/24 [.OMEGA.]).times.0.01
[s]=4.16 [Ws].
[0105] FIG. 13 is a view illustrating a relationship between AC
voltage waveforms applied to each of the heating elements and the
control signals for turning on the triacs 550 and 551 in a state
where the usage proportions of the heating elements 541 and 542 and
the heating element 543 is 50%:50%. In FIG. 13, eight half-waves of
the AC voltage waveform are set as a control unit. In FIG. 13,
power supply is performed to the heating elements 541 and 542 for
0.08 s (=0.01 [s/half-wave].times.8 [half-waves]) which is the time
corresponding to eight half-waves, and thereafter, the power supply
destination is switched to the heating element 543. Thereafter,
power supply is performed to the heating element 543 for 0.08 s,
which corresponds to the time corresponding to eight half-waves,
before the power supply destination is switched back to the heating
elements 541 and 542.
[0106] In order to apply AC voltage to the heating elements 541 and
542, the CPU 94 counts a number of times T1 the control signal has
been output to the triac 550, and every time the control signal is
output, an electrical energy of 9.52 [Ws] is added to the
accumulated electrical energy. IWS1 of the heating elements 541 and
542. An accumulated electrical energy IWSb1 at the area of the
non-sheet-passing portion when the heating elements 541 and 542 are
used can be calculated by the expression IWSb1=accumulated
electrical energy IWS1.times.(length hb1 of non-sheet-passing
portion of the healing elements 541 and 542/heating element length
H1 of the heating elements 541 and 542). Similarly, in order to
apply AC voltage to the heating element 543, the CPU 94 counts a
number of times T2 the control signal has been output to the triac
551, and every time the control signal is output, electrical energy
of 4.16 [Ws] is added to the accumulated electrical energy IWS2 of
the heating element 543. An accumulated electrical energy IWSb2 at
the area of the non-sheet-passing portion when the heating element
543 is used can be calculated by the expression IWSb2=accumulated
electrical energy IWS2.times.(length hb2 of non-sheet-passing
portion of the heating element 543/heating element length H2 of the
heating element 543). Then, the CPU 94 calculates the accumulated
electrical energy IWSb of the non-sheet-passing portion of the
heater 54 by adding the accumulated electrical energy IWSb1 of the
non-sheet-passing portion of the heating elements 541 and 542 being
calculated and the accumulated. electrical energy IWSb2 of the
non-sheet-passing portion of the healing element 543.
Relationship between Accumulated Electrical Energy at
Non-Sheet-Passing Portion of Heater and Risen Temperature Value of
Non-Sheet-Passing Portion of Fixing Film
[0107] FIG. 14A is a graph showing a time transition of the
accumulated electrical energy IWSb in the area of the
non-sheet-passing portion of the heater 54 in a state where the
warm-up level of the fixing unit 50 is 1 (Lv1), that is, in a state
where the ratio of the usage proportions of the heating elements
541 and 542 to the usage proportion of the heating element 543 is
50%:50%. In FIG. 14A, the vertical axis indicates the accumulated
electrical energy IWSb (unit: Ws) in the area of the
non-sheet-passing portion of the heater 54, and the horizontal axis
indicates time (unit: s). Since the lengths of the heating elements
differ, the electrical energies at the area of the
non-sheet-passing portion of the heater 40 during use of the
heating elements 541 and 542 and that during use of the heating
element 543 differ. Further, as described above, since the heating
elements 541 and 542 and the heating element 543 are used
alternately, as illustrated in FIG. 14A, the accumulated electrical
energy IWSb at the area of the non-sheet-passing portion is
transited in steps. As described in the first and second
embodiments, the CPU 94 calculates an inclination a based on the
time transition of accumulated electrical energy, wherein the
inclination .alpha. of the graph shown in FIG. 14A was 14.9. When
the risen temperature saturation value in a state where the
inclination .alpha. is 14.9 is calculated as Y=7.4X+156, which is
the relational expression 2 of FIG. 7B explained in the first
embodiment, the risen temperature saturation value is calculated as
266.degree. C. (.apprxeq.7.4[.degree. C.]14.9+156[.degree. C.].
[0108] Next, if the risen temperature value at the area of the
non-sheet-passing portion is higher than the risen temperature
saturation value according to the relational expression 1
(Y=0.23X+150) according to FIG. 7A of the first embodiment, the
risen temperature saturation value calculated by the relational
expression 2 is substituted in the risen temperature value at the
area of the non-sheet-passing portion of the relational expression
1. FIG. 14B is a graph illustrating a relational expression 3 which
shows the relationship between the accumulated electrical energy
(unit: Ws) of the non-sheet-passing portion of the heater 54 and
the risen temperature value (unit: .degree. C.) of the
non-sheet-passing portion of the fixing film 51 after substituting
the risen temperature saturation value. The CPU 94 calculates the
risen temperature value of the non-sheet-passing portion of the
fixing film 51 after printing is ended based on the relational
expression 3 and the accumulated electrical energy at the area of
the non-sheet-passing portion of the heater 54 after printing is
ended. Then, similarly to the first and second embodiments, the CPU
94 determines the cooling time of the fixing unit 50 based on the
risen temperature value at the non-sheet-passing portion of the
fixing film 51 being calculated and executes the cooling operation
to the fixing unit 50. The above-described explanation illustrates
the case where the B5-size sheet was passed, but similar procedures
can be taken in a case where an A5-size sheet using the heating
elements 541 and 542 and the heating element 544 is passed through.
Though it is necessary to change the processing for calculating the
accumulated electrical energy of the non-sheet-passing portion of
the heating element in the flowchart shown in FIG. 9 illustrating
the first embodiment, the flowchart of FIG. 9 can also be applied
to the third embodiment.
[0109] As described above, according to the present embodiment,
even if the heater 54 includes a plurality of heating elements
having different lengths, the electrical energy of the
non-sheet-passing portion of the entire heater 54 is calculated
based on the electrical energy of the non-sheet-passing portion of
each of the heating elements. By calculating the electrical energy
of the non-sheet-passing portion of the entire heater 54, similarly
to the first and second embodiments, the risen temperature value of
the non-sheet-passing portion of the fixing member can be
calculated accurately based on the accumulated electrical energy of
the non-sheet-passing portion of the heating element and the risen
temperature saturation value of the non-sheet-passing portion.
Thereby, the cooling time of the fixing unit after passing through
the small-size sheet can be shortened. Then, by executing the
cooling of the fixing member appropriately according to the
temperature of the fixing member, the occurrence of a hot offset
that may occur when passing through a large-size sheet after
passing through a small-size sheet can be reduced.
[0110] As described, according to the present embodiment, a period
of rotation of the pressure roller for cooling the fixing member
can be controlled according to the temperature of the
non-sheet-passing portion of the fixing member of the fixing
unit.
Fourth Embodiment
[0111] According to the first to third embodiments described above,
the risen temperature value at the area of the non-sheet-passing
portion is calculated based on the electrical energy supplied to
the non-sheet-passing portion of the heating elements of the
heater, and the cooling time of the fixing unit was determined
based on the calculated risen temperature value. The fourth
embodiment describes a method for calculating a risen temperature
saturation value of the heating elements of the heater by a simple
method and determining the cooling time of the fixing unit by
setting the calculated risen temperature saturation time as a risen
temperature value of the area of the non-sheet-passing portion will
be explained. The configurations of the image forming apparatus,
the fixing unit, and the heater according to the present embodiment
are similar to the third embodiment, so that by assigning the same
reference numbers to the same units and members, the descriptions
thereof are omitted.
Relationship between Usage Proportions of Heating Elements and
Risen Temperature Saturation Value when Passing Through B5-size
Sheet
[0112] Using B5-size sheets, a sheet passing test for confirming
the relationship between the usage proportion of the heating
elements 541 and 542 and that of the heating element 543 and the
risen temperature saturation value at the area of the
non-sheet-passing portion of the fixing film 51 was performed. The
usage proportions of the heating elements 541 and 542 and the
heating element 543 was divided into four patterns according to the
warm-up levels 1 to 4 of the fixing unit 50, similarly to Table 1
described earlier. In the sheet passing test, a B5-size sheet
having a grammage of 128/m.sup.2 was used, temperature control was
executed so that the detection temperature of the thermistor 60
arranged in contact with the heater 54 is maintained at 200.degree.
C., the sheet conveyance speed was set to 200 mm/sec, and the feed
interval of the sheets was set to 0.2 s.
[0113] Table 2 is a table that summarizes the results of the sheet
passing test of B5-size sheets. Table 2 is composed of warm-up
levels (1 to 4) of the fixing unit 50, usage proportions (unit: %)
of the heating elements 541 and 542 and the heating element 543
corresponding to the warm-up levels when passing through B5-size
sheets, and risen temperature saturation values (unit: .degree. C.)
corresponding to the warm-up level of the area of the
non-sheet-passing portion of the fixing film 51. As illustrated in
Table 2, the usage proportions of the heating elements 541 and 542
and the heating element 543 according to warm-up level 1 was
50%:50%, and the risen temperature saturation value was 227.degree.
C. Similarly, the usage proportions of the heating elements 541 and
542 and the heating element 543 according to warm-up level 2 was
30%:70%, and the risen temperature saturation value at that time
was 211.degree. C. Moreover, the usage proportions of the heating
elements 541 and 542 and the heating element 543 according to
warm-up level 3 was 20%:80%, and the risen temperature saturation
value at that time was 203.degree. C. The usage proportions of the
heating elements 541 and 542 and the heating element 543 according
to warm-up level 4 was 10%:90%, and the risen temperature
saturation value was 195.degree. C.
TABLE-US-00002 TABLE 2 USAGE PROPORTION OF HEATING ELEMENT [%]
RISEN FIXING UNIT HEATING HEATING TEMPERATURE WARM-UP ELEMENTS
ELEMENT SATURATION LEVEL 541, 542 543 VALUE [.degree. C.] 1 50 50
227 2 30 70 211 3 20 80 203 4 10 90 195
[0114] FIG. 15A is a graph plotting risen temperature saturation
values corresponding to the usage rate of the heating element 543
shown in Table 2, wherein the vertical axis indicates a risen
temperature saturation value (unit: .degree. C.) of the fixing film
51, and the horizontal axis indicates usage rate (unit: %) of the
heating element 543. As illustrated in FIG. 15A, it can be
recognized that there is a high correlation between the usage rate
of the heating element 543 and the risen temperature saturation
value. If a straight line connecting the points plotted in FIG. 15A
is defined as a relational expression 4 of a case where B5-size
sheets are passed through, the relational expression 4 can be
represented by Y=-0.8X+267 when the usage rate of the heating
element 543 is X and the risen temperature saturation value is
Y.
Relationship between Usage Proportions of Heating Elements and
Risen Temperature Saturation Value when Passing Through A5-size
Sheet
[0115] Using A5-size sheets, a sheet passing test for confirming
the relationship between the usage proportions of the heating
elements 541 and 542 and the heating element 544 and the risen
temperature saturation value at the area of the non-sheet-passing
portion of the fixing film 51 was performed. The usage proportions
of the heating elements 541 and 542 and the heating element 544 was
divided into four patterns according to the warm-up levels 1 to 4
of the fixing unit 50, similarly to Table 1 described earlier. In
the sheet passing test, an A5-size sheet having a grammage of 128
g/m.sup.2 was used, temperature control was executed so that the
detection temperature of the thermistor 60 arranged in contact with
the heater 54 is maintained at 200.degree. C., the sheet conveyance
speed was set to 200 mm/sec, and the feed interval of the sheets
was set to 0.2 s.
[0116] Table 3 is a table that summarizes the results of the sheet
passing test of A5-size sheets. Table 3 is composed of warm-up
levels (1 to 4) of the fixing unit 50, usage proportions (unit: %)
of the heating elements 541 and 542 and the heating element 544
corresponding to the warm-up levels when passing through A5-size
sheets, and risen temperature saturation values (unit: .degree. C.)
corresponding to the warm-up level of the area of the
non-sheet-passing portion of the fixing film 51. As illustrated in
Table 3, the usage proportions of the heating elements 541 and 542
and the heating element 544 according to warm-up level 1 was
50%:50%, and the risen temperature saturation value was 220.degree.
C. Similarly, the usage proportions of the heating elements 541 and
542 and the heating element 544 according to warm-up level 2 was
30%:70%, and the risen temperature saturation value at that time
was 204.degree. C. Moreover, the usage proportions of the heating
elements 541 and 542 and the heating element 544 according to
warm-up level 3 was 20%:80%, and the risen temperature saturation
value at that time was 196.degree. C. The usage proportions of the
heating elements 541 and 542 and the heating element 544 according
to warm-up level 4 was 10%:90%, and the risen temperature
saturation value was 185.degree. C.
TABLE-US-00003 TABLE 3 USAGE PROPORTION OF HEATING ELEMENT [%]
RISEN FIXING UNIT HEATING HEATING TEMPERATURE WARM-UP ELEMENTS
ELEMENT SATURATION LEVEL 541, 542 544 VALUE [.degree.C] 1 50 50 220
2 30 70 204 3 20 80 196 4 10 90 185
[0117] FIG. 15B is a graph plotting risen temperature saturation
values corresponding to the usage rate of the heating element 544
shown in Table 3, wherein the vertical axis indicates a risen
temperature saturation value (unit: .degree. C.) of the fixing film
51, and the horizontal axis indicates usage rate (unit: %) of the
heating element 544. As illustrated in FIG. 15B, it can be
recognized that there is a high correlation between the usage rate
of the heating element 544 and the risen temperature saturation
value. If a straight line connecting the points plotted in FIG. 15B
is defined as a relational expression 4, i.e., third calculation
formula, of a case where A5-size sheets are passed through, the
relational expression 4 can be represented by Y=-0.86X+263.6 when
the usage rate of the heating element 544 is X and the risen
temperature saturation value is Y.
[0118] Also regarding sheets of other sizes, the sheet passing test
is performed in a similar method, and the relational expression 4
corresponding to each of the sheets is calculated. Then, the
calculated relational expression is stored in the memory 95
including relational expressions 4 for the B5-size and A5-size
sheets. According to the present embodiment, the risen temperature
saturation value at the non-sheet-passing portion of the fixing
film 51 is calculated based on the relational expression 4 stored
in advance in the memory 95 and the usage proportions of the
heating elements 543 and 544 according to the warm-up level. Then,
the calculated risen temperature saturation value is set as the
risen temperature value of the non-sheet-passing portion of the
fixing film 51, and the cooling time corresponding to the risen
temperature value of the non-sheet-passing portion is
determined.
Control Sequence of Cooling of Fixing Unit
[0119] FIG. 16 is a flowchart illustrating a control sequence of
cooling for lowering the risen temperature value of the
non-sheet-passing portion of the fixing film 51 of the fixing unit
50 according to the present embodiment. The procedure illustrated
in FIG. 16 is started and executed by the CPU 94 when priming to
the sheet P is performed. The CPU 94 performs temperature control
of the fixing film 51 of the fixing unit 50 by controlling the
power supply to the heating elements 541, 542, 543, and 544 of the
heater 54 based on the usage proportions shown in Tables 2 and 3
mentioned above. Further, the temperature control of the fixing
film 51 of the fixing unit 50 is executed by a different processing
as the processing illustrated in the flowchart of FIG. 16. Further,
it is assumed that the information of tables 2 and 3 described
above and the relational expression 4 are already stored in the
memory 95. Further, it is assumed that the memory 95 stores a table
associating the risen temperature value of the non-sheet-passing
portion of the fixing film 51 with a cooling time for lowering the
temperature of the non-sheet-passing portion of the fixing film 51
to a predetermined temperature. The print job performed by the
print command from the PC 110 is assumed to be the print job to the
sheets P having the same sheet size.
[0120] In S200, the CPU 94 acquires a sheet type information, such
as B5-size or A5-size, of the sheet P, based on the information on
the sheet P included in the print command received from the video
controller 91. Further, the CPU 94 determines the warm-up level (1
to 4) of the fixing unit 50 based on the temperature of the heater
40 detected by the thermistor 60. In S201, the CPU 94 acquires the
usage proportions of the heating elements based on table 2 or table
3 stored in the memory 95 based on the sheet type information of
the sheet P acquired in S200 and the warm-up level of the fixing
unit 50 determined in S200. For example, if the sheet used for the
print job is a B5-size sheet, the CPU 94 acquires the usage
proportion of the heating element 543 corresponding to the warm-up
level of the fixing unit 50 using table 2. Similarly, if the sheet
used for the print job is an A5-size sheet, the CPU 94 acquires the
usage proportion of the heating element 544 corresponding to the
warm-up level of the fixing unit 50 using table 3.
[0121] In S202, the CPU 94 reads the relational expression 4
corresponding to the heating element of the usage proportions
acquired in S201 from the memory 95 and substitutes the
corresponding usage proportions of the heating elements to the
relational expression 4, by which the risen temperature saturation
value of the fixing film 51 is calculated. In S203, the CPU 94
determines whether the print job has ended, wherein if it is
determined that the print job has ended, the procedure advances to
S204, and if it is determined that the print job is not ended, the
procedure returns to S203.
[0122] In S204, the CPU 94 determines the risen temperature
saturation value of the fixing film 51 calculated in S202 as the
risen temperature value of the area of the non-sheet-passing
portion of the fixing film 51. In S205, the CPU 94 acquires the
cooling time corresponding to the risen temperature value of the
non-sheet-passing portion of the fixing film 51 determined in S204
from the table associating the risen temperature value of the
non-sheet-passing portion of the fixing film 51 stored in the
memory 95 with the cooling time of the fixing film 51.
[0123] In S206, the CPU 94 stops the pressure roller 53 of the
fixing unit 50, and resets and start the timer. In S207, the CPU 94
refers to the timer, and determines whether the timer value has
passed the cooling time. If the CPU 94 determines that the timer
value has not passed the cooling time, the procedure returns to
S207, and if it determines that the timer value has exceeded the
cooling time, the procedure is ended. During the cooling time, a
process of stopping rotation of the pressure roller 53 to lower the
temperature of the non-sheet-passing portion of the fixing film 51
was performed. Alternatively, during cooling time, it is possible
to rotate the pressure roller 53 to lower the temperature of the
non-sheet-passing portion of the fixing film 51 and to perform a
processing to stop rotation of the pressure roller 53 after the
cooling time has elapsed.
[0124] As described, according to the present embodiment, the risen
temperature saturation value of the fixing film 51 is calculated
based on usage proportions of the heating elements determined based
on the sheet size being used and the warm-up level of the fixing
unit, and the calculated risen temperature saturation value is set
as the risen temperature value of the non-sheet-passing portion.
According to the fourth embodiment, the risen temperature value of
the non-sheet-passing portion of the fixing film 51 is determined
by a simple method, so that the accuracy of the risen temperature
value of the non-sheet-passing portion is deteriorated and the
cooling time is elongated compared to the first to third
embodiments described earlier. However, since the cooling time
corresponding to the warm-up level of the fixing unit 50 is
ensured, the occurrence of hot offsets can be reduced.
[0125] As described above, according to the present embodiment, the
period of rotation of the pressure roller for cooling the fixing
member can be controlled according to the temperature of the
non-sheet-passing portion of the fixing members of the fixing
unit.
[0126] According to the technique of the present disclosure, the
period of rotation of the pressure roller for cooling the fixing
member can be controlled according to the temperature of the
non-sheet-passing portion of the fixing members of the fixing
unit.
Other Embodiments
[0127] Embodiment(s) of the present invention can also be realized
by a computer of a system or apparatus that reads out and executes
computer executable instructions (e.g., one or more programs)
recorded on a storage medium (which may also be referred to more
fully as a `non-transitory computer-readable storage medium`) to
perform the functions of one or more of the above-described
embodiment(s) and/or that includes one or more circuits (e.g.,
application specific integrated circuit (ASIC)) for performing the
functions of one or more of the above-described embodiment(s), and
by a method performed by the computer of the system or apparatus
by, for example, reading out and executing the computer executable
instructions from the storage medium to perform the functions of
one or more of the above-described embodiment(s) and/or controlling
the one or more circuits to perform the functions of one or more of
the above-described embodiment(s). The computer may comprise one or
more processors (e.g., central processing unit (CPU), micro
processing unit (MPU)) and may include a network of separate
computers or separate processors to read out and execute the
computer executable instructions. The computer executable
instructions may be provided to the computer, for example, from a
network or the storage medium. The storage medium may include, for
example, one or more of a hard disk, a random-access memory (RAM),
a read only memory (ROM), a storage of distributed computing
systems, an optical disk (such as a compact disc (CD), digital
versatile disc (DVD), or Blu-ray Disc (BD).TM.), a flash memory
device, a memory card, and the like.
[0128] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
[0129] This application claims the benefit of Japanese Patent
Application No. 2021-040563, filed on Mar. 12, 2021, which is
hereby incorporated by reference herein in its entirety.
* * * * *